(OSA) is a relatively common disorder that interrupts the continuity of sleep. OSA leads to cognitive impairment, daytime sleepiness, increased risk of automobile accidents, and diminished quality of life. Patients with schizophrenia have multiple risk factors for OSA including obesity and sedating medications and often presents with somnolence. In addition, the atypical antipsychotic medications may increase the risk of OSA because of weight gain. Among the serious potential consequences of OSA in schizophrenia is impaired cognitive functioning. Diminished cognitive functioning is a core characteristic of schizophrenia that is associated with poorer community functioning. Cognition can be further impaired by OSA and resultant daytime sleepiness. Relieving co-morbid OSA when present in schizophrenia might reduce the overall sleepiness of patients on atypical antipsychotics. This application proposes a treatment study of sleep apnea in patients with schizophrenia using (CPAP), the treatment of choice for moderate to severe OSA. The study hopes to determine whether aggressive treatment of OSA-induced daytime sleepiness with this non-invasive, non-drug technique can significantly improve performance on cognitive tasks, psychotic symptoms, daytime sleepiness, and quality of life. The results of this research have the potential to support the importance of recognizing and treating daytime sleepiness among a subgroup of people with severe and persistent mental illness.